There's a crack forming on Rosetta's 67P: Is it breaking up?

A fissure spanning over 100 meters across the neck of Rosetta’s comet 67P raises the question of if, or when, the comet will break up. The fissure is part of released studies by Rosetta scientists in the journal Science. Credit: ESA/Rosetta, Illustration, T.Reyes

Not all comets break up as they vent and age, but for Rosetta's comet 67P, the Rubber Duckie comet, a crack in the neck raises concerns. Some comets may just fizzle and uniformly expel their volatiles throughout their surfaces. They may become like puffballs, shrink some but remain intact.

Comet 67P is the other extreme. The expulsion of volatile material has led to a shape and a point of no return; it is destined to break in two. Songwriter Neil Sedaka exclaimed, "Breaking Up is Hard to Do," but for comets this may be the norm. The fissure is part of the analysis in a new set of science papers published this week.

The images show a fissure spanning a few hundred meters across the neck of the two lobe comet. The fissure is just one of the many incredible features on Comet 67P and is reported in research articles released in the January 22, 2015, edition of the journal Science.

What it means is not certain, but Rosetta team scientists have stated that flexing of the comet might be causing the fissure. As the comet approaches the Sun, the solar radiation is raising the temperature of the surface material. Like all materials, the comet's will expand and contract with temperature. And diurnal (daily) changes in the tidal forces from the Sun is a factor, too.

The crack, or fissure, could spell the beginning of the end for comet 67P/Churyumov–Gerasimenko. It is located in the neck area, in the region named Hapi, between the two lobes that make 67P appear so much like a Rubber Duck from a distance. The fissure could represent a focal point of many properties and forces at work, such as the rotation rate and axis – basically head over heels of the comet. The fissure lies in the most active area at present, and possibly the most active area overall. Though the Hapi region appears to receive nearly constant sunlight, at this time, Rosetta measurements (below) show otherwise – receiving 15% less sunlight than elsewhere.

Top left: The Hathor cliff face is to the right in this view. The aligned linear structures can be clearly seen. The smooth Hapi region is seen at the base of the Hathor cliff. Boulders are prevalent along the long axis of the Hapi region. Bottom left and right: Crack in the Hapi region. The left panel shows the crack (indicated by red arrows) extending across Hapi and beyond. The right panel shows the crack where it has left Hapi and is extending into Anuket, with Seth at the uppermost left and Hapi in the lower left. Credit: ESA/Rosetta

Sunlight and heating are major factors and the neck likely experiences the greatest mechanical stresses – internal torques – from heating or tidal forces from the sun as it rotates and approaches perihelion. Rosetta scientists are still not certain whether 67P is two bodies in contact – a contact binary – or a shape that formed from material expelled about the neck area leading to its narrowing.

The Philae lander's MUPUS thermal sensor measured a temperature of –153°C (–243°F) at the landing site, while VIRTIS, an instrument on the primary spacecraft Rosetta, has measured -70°C (-94°F) at present. These temperatures will rise as perihelion is reached on August 13, 2015, at a distance of 1.2432 A.U. (24% further from the Sun than Earth). At present – January 23rd – 67P is 2.486 A.U. from the Sun (2 1/2 times farther from the Sun than Earth). While not a close approach to the Sun for a comet, the Solar radiation intensity will increase by 4 times between the present (January 2014) and perihelion in August.

Stresses due to temperature changes from diurnal variations, the changing Sun angle during perihelion approach, from loss of material, and finally from changes in the tidal forces on a daily basis (12.4043 hours) may lead to changes in the fissure causing it to possibly widen or increase in length. Rosetta will continue escorting the comet and delivering images of the whole surface that will give Rosetta scientists the observations and measurements to determine 67P/Churyumov–Gerasimenko's condition now and its fate in the longer term.

Left: A map looking at the northern (right-hand rule, positive,) pole of 67P showing the total energy received from the Sun per rotation on 6 August 2014. The base of the neck (Hapi) receives ~15% less energy than the most illuminated region, 3.5 × 106 J m-2 (per rotation). If self-heating were not included, the base of the neck would receive ~30% less total energy. Right: Similar to the left panel but showing total energy received over an entire orbital period in J m-2 (per orbit). Credit:ESA/Journal Science Article, Figure 5

Fragmentation of comets is common. Many sungrazers are broken up by thermal and tidal stresses during their perihelions. At top, an image of the comet Shoemaker-Levy 9 (May 1994) after a close approach with Jupiter which tore the comet into numerous fragments. An image taken by Andrew Catsaitis of components B and C of Comet 73P/Schwassmann–Wachmann 3 as seen together on 31 May 2006. Credit: NASA/HST, Wikipedia, A. Catsaitis

Hubble captured a sequence of images of the comet 73P/Schwassman-Wachmann 3. The comet fragmented, and like 73P, Rosetta’s 67P will likely break some day into two major fragments with debris spreading out as in these images. The Solar wind pressure, as well as any explosive force from the break up, will cause the comet fragments to slowly disperse but effectively remain in the same orbit. Credit: NASA/Hubble

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11 comments

Why do we take such leaps when given such paltry info? A crack must equal coming apart? We have observed this multi-billion year old object for a few weeks and we immediately start positing things based on the paltriest of data. I thought I saw evidence of ancient water on its surface, or in some areas it appears geologically active. Both those things are ridiculous and no one would make those leaps based on the size of the object, but the tendency to generalize is there and that's what we do with every bit of new info. Let's collect some more data before theorizing.

Why do we take such leaps when given such paltry info? A crack must equal coming apart?

Because the orbital period of the comet is 6.45 years, and each time it passes near the sun it gets an atmosphere of dust and vapors, some of which end up landing back on the surface as it recedes from the sun. Every 6½ years its surface gets blown off and re-deposited, so any open cracks must have been opened in the last few years.

And that points out to significant internal stresses caused by some outside force acting on the comet, and since it's not likely to be a one-off incident but repeating every orbit, it's likely that the crack will keep growing and eventually split the comet.

Why do we take such leaps when given such paltry info? A crack must equal coming apart? We have observed this multi-billion year old object for a few weeks and we immediately start positing things based on the paltriest of data. I thought I saw evidence of ancient water on its surface, or in some areas it appears geologically active. Both those things are ridiculous and no one would make those leaps based on the size of the object, but the tendency to generalize is there and that's what we do with every bit of new info. Let's collect some more data before theorizing.

Nobody is theorizing anything and no one is generalizing. Scientist have detected a significant crack and because comets have been observed breaking up they are just suggesting that might be 67P's fate.

Losik

Jan 27, 2015

This comment has been removed by a moderator.

Losik

MO the mutual friction of their parts due to tidal forces is the main source of their heating

There's not nearly enough movement for that. Try shaking a plastic bottle full of sand really hard until it gets 1 degrees C hotter. Makes for a great workout as well. It takes enormous amounts of energy to actually evaporate most stuff, even though it may have a very low boiling point.

Furthermore, the tidal heating with planets and moons comes from there being enough mass and gravity that rock or ice or whatever starts to flow under the pressure instead of behaving like a solid. This churning of a viscous mass is what effectively converts it to heat.

With a bunch of large boulders and a bit of dust in between, it's less like mixing treacle, and more like rubbing a bunch of pebbles in a bag - they jam and tangle instead of rub and slide.

The neck of comet is generating most of gases despite it's in shadow

Looks very much sunlit to me.

Losik

A volcano implies tectonic activity, which requires a molten mantle. The comet definitely doesn't have one because it's too small. It loses heat too fast to maintain one, and it has no internal heat source. If there was an internal heat source to maintain a semi-liquid state mantle for volcanic activity, it would re-shape the comet into a ball, and the crust would be mere inches thick.

If there is something resembling a volcano, it's a pocket of frozen gasses covered with mineral dust.

Losik

Come on zeph, admit you're just joking about the volcano and the plant growing on 67P. We all know your scientific views are, shall we say unconventional, but you can't possibly be serious about 67P. Right?

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